Catalytic cracking of hydrocarbons



April 24, 1951 L. PELZER ET AL CATALYTIC CRACKING 0F HYDROCARBONS Filed June 27, 1947 46 $55 2% .6553 SGEEBE HOiVHEINI-IQEIH HOLVNOILQVHA HOLOVBH aoiovaa HOLVNOILQVHA INVENTORS HARRY LOUIS PELZER AND KENNETH MERLE WATSON ATTORN EYS Patented Apr. 24,1951

CATALYTIC CRACKING OF HYDROCARBONS Harry Louis Pelzer, Steger, Ill., and Kenneth Merle Watson, Madison, Wis., assignors to Sinclair Refining Company, New York, N. Y., a corporation of Maine 1 Application June 27; 1947, Serial No. 757,651

This invention relates to the pyrolytic cracking of hydrocarbons and, more particularly, to such processes wherein the hydrocarbons are cracked in the presence of a solid catalyst.

The invention provides an improved catalytic cracking process especially useful in the cracking of heavier hydrocarbon distillates, gas oil for instance, to produce a lighter, lower boiling fraction within the motor fuel, or gasoline, range.

- In a once-through cracking operation, even under most advantageous conditions, only a portion of the charging stock is cracked to the desired product. In addition to constituents within the desired boilin range, the effluent from the cracking reaction zone contains a relatively large amount of higher boiling hydrocarbons and it iscustomary to separate the lighter from the heavier hydrocarbon constituents by fractional tially different from those of the fresh virgin charge oil; Usually, the recycle stock is more resistant to cracking, or further cracking, than the fresh charge 011. a

If these more highly refractory insufficiently cracked ;.constituents of the eflluent vapors ,ar'e' recharged-11:0 the cracking zone, together with the virgin gas-oil, for instance, in which conditions optimum forthe cracking of the gas oil are maintained, they will undergo little or no decomposition and will accumulate in the system, and if cracking conditions optimum for their cracking are maintained in the cracking zone, the gas oil will be overcracked.

In accordance with our present invention, these and other objectionable conditions are avoided in a catalytic cracking unit by separately cracking the virgin charge oil and the recycle stock in separate reactors. Advantageously, theconstituents of the efiluent vapors from the cracking of the virgin stock which are heavier than the desired product are fractionated to form a heavierv and a lighter recycle stock and these fractions are subjected to different cracking conditions as by injecting them into diflerent zones of thesecond reactor. Catalyst which has been used in 2 Claims. (01. lea-52) the cracking of the virgin charge stock in the first reactor is, with advantage, passed to the applicable to processes involving moving beds of non-fiuidized catalyst in which hot, freshly'regenerated catalyst is supplied to the upper end of the bed and spent catalyst is withdrawn from the lower end of the bed for regeneration.

The invention will be further described and illustrated with reference to the accompanying drawing Which represents conventionally and diagrammatically a flow diagram of the fluid catalyst cracking operation embodying my invention'. r I

Inthe operation shown in the drawing, a virgin charge oilfgas oil for instance, is passed to the system through line I, is admixed with catalyst passing through line 2 from regenerator 3 to form .a suspension which is passed upwardly into the lower end of reactor 4'. Products of the cracking reaction pass from reactor 4 through line 5 to the fractionator 6 in which a lighter fraction containin the desired product is separated and passes as a vapor from the upper end of the fractionator through line 1. A

heavier fraction is withdrawn from the lower end" of the fractionator through line 8 and an intermediate fraction withdrawn as a side stream through line 9.

Catalyst which has been used in the reactor 4, passes therefrom through line In into line 9 and is caught up in suspension in the intermediate fraction and carried upwardly into the reactor II. The heavier fraction, withdrawn from the lower end of the fractionator, is passed through line 8 into an intermediate zone of the reactor l I.

Spent catalyst is withdrawn from reactor ll through line l2 and passed to regenerator 3 wherein the catalyst is regenerated and returned to reactor 4 for further contact with fresh virgin charge oil. Hydrocarbon vapors, withdrawn from reactor ll, pass through line I3 to fractionator M from which the lighter constituents are withdrawn through line l5 and the heavier condensate withdrawn through line I 6.

By the operation shown, a higher gasoline yield and a lower over-all coke formation is attained than is attained in known equivalent, recycle, or once-through operations yieldin higher than 40% of the desired product. The present process will produce yields within the range of 40 to The invention contemplates known means for conveying the catalyst, regenerating the catalyst and effecting contact between the catalyst and the respective gases and vapors and need not here be described in detail. In general, the regeneration may be effected by passing air in contact with the spent catalyst whereby carbonaceous deposit formed thereon during the cracking operation is burned. In a fluid cracking operation, the catalyst is conveyed in fluid suspension in a suitable gaseous medium. and in. the so-called moving bed process of the T. C. C. type, conventional conveying means may be employed.

The catalyst used may be the type convenztionally used in cracking processes. In the application of the present invention to fluid catalyst processes, the catalyst used may, for instance, be a silica-alumina type catalyst in finely divided or powdered form. The reaction. conditions may, likewise, be those conventionally used in operations of this general type and, as under-- stood by the art, the optimum temperatures and pressures will depend primarily upon the type ofv feed stock used, the particular catalyst employed and the depth of. cracking required.-

In cracking gas oil, for instance, the reaction temperature may, with advantage, be within the range of about 800 to 1,000F. and the pressure at the top of the reactor within the range of about to 25 pounds per square inch. Thev regeneration temperature is, with advantage, within the range of about 950 to 1,200 F., heat for the reaction being supplied, in large measure at least, by the hot regenerated catalyst.

Usually, the charge oil will be preheated and vaporized, or partialy vaporized, before being mixed with. the catalyst from the regenerator. The recycle stock from fractionator 6 may, likewise, be preheated and vaporized, or partially vaporized, before being passed to the reactor ll.

Cracking conditions maintained in the second reactor will normally be more severe than those maintained in the first reactor, optimum conditions depending upon the characteristics of the recycle stock. The more refractory intermediate fractions passing to the lower end of the second reactor will ordinarily be subject to more severe cracking conditions than the fraction of recycle stock passed to the intermediate zone of the second reactor.

The amount of recycle stock passed to the 4 second reactor will ordinarily be substantially less than the amount of virgin charge oil passed to the first reactor. The amount of catalyst used for each of the reactors will ordinarily be the same. Consequently, the catalyst-oil ratio in the second reactor may be substantially greater than that in the first reactor, resulting in more serve cracking conditions in thesecond reactor.

Where higher temperatures are desired in the second reactor than in the first reactor, heat may be supplied to the. second reactor by known means, for instance, by strongly preheating the recycle stock passing thereto from the fractionator 6.

We claim:

1. In a process for the catalytic cracking of -hydrocarbons wherein the hydrocarbons are passed in contact with a cracking catalyst in a conversion chamber and the efiluent vapors therefrom are fractionated to form an insufficiently cracked fraction heavier than the desired fraction and which is subjected to further cracking, the steps of separating the insufficiently cracked fraction into a heavier and a lighter fraction, introducing the lighter fraction. into 2. The process of, claim 1 in which the cata lyst-oil ratio in the separate conversion chamber is in excess of that in the first conversion chama ber HARRY LOUIS PELZE-R. KENNETH MERLE WATSON.

' REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,345,753 Kinneberg Apr. 4, 1944 2,379,159 Kanhofer June 26, 1945 2,419,519 Evans Apr. 22, 1947 2,432,277

Brackenbury Q. A Dec. 9, 1947 

